Site 1266 (proposed Site WALV-10F) is located on the northwestern flank of Walvis Ridge. At a water depth of 3806 m, the site is ~20 m shallower than Deep Sea Drilling Project (DSDP) Site 528 to the north, where previous drilling recovered a 470-m-thick section of Neogene, Paleogene, and Maastrichtian sediment (Moore, Rabinowitz, et al., 1984). Sediment composition at Site 528 is relatively uniform, predominantly carbonate rich oozes and chalks with a few thin intervals of nannofossil clays. The Miocene–Pleistocene section consists of foraminiferal nannofossil oozes and extends from the seafloor to ~170 meters below seafloor (mbsf). The Oligocene section also consists of foraminiferal nannofossil ooze and extends to 225 mbsf. The Paleocene–Eocene sequence extends from 225 to 410 mbsf and consists of nannofossil oozes and chalks and clays. The Paleocene/Eocene (P/E) boundary was not recovered at this site, although an expanded Cretaceous/Paleogene (K/P) boundary was. A few thin disseminated layers of chert were encountered in the upper Paleocene between 330 and 400 mbsf. The sediments immediately above basement are of middle Maastrichtian age. Site 528 was rotary cored and, as a consequence, recovery was poor (63%) and much of the core suffered from severe drilling disturbance, particularly the unlithified Neogene and Paleogene oozes.
Our main objective for this site was the recovery of undisturbed sediments recording critical intervals in the early Cenozoic, specifically the Paleocene/Eocene Thermal Maximum, and the period of global cooling and growth of polar ice caps across the Eocene/Oligocene (E/O) boundary into the earliest Oligocene (early Oligocene Glacial Maximum). We planned to recover 100% of the sedimentary section in multiple holes to make it possible to establish a cyclostratigraphy and develop an astronomically tuned timescale. We aimed to fully document events across the critical intervals as well as short episodes of climate fluctuation during the early Eocene Climatic Optimum.
Site 1266 is the approximate midpoint of the Leg 208 depth transect and is at a depth where fluctuations in depth of the calcite compensation depth are registered in the sediment. To optimize recovery of the P/E boundary, Site 1266 was located in an area where the Neogene sediments are thin. In this location, overall sediment thickness is ~400 m (common depth point 12,900 on line GeoB 01-030) (Figs. F1, F2, both in the "Leg 208 Summary" chapter; Fig. F1). The site sits along the edge of a north-south–trending channel. Seismic profiles show several packages of reflectors, which we describe as upper (0–105 ms two-way traveltime [TWT] below seafloor), middle (105–230 ms TWT below seafloor), and lower (230–430 ms TWT below seafloor) (Figs. F2, F3). The upper package, which is thinner than the upper package at Site 528, consists of middle Miocene–Pleistocene calcareous oozes; the middle package consists of Oligocene and lower Miocene calcareous oozes and clays; and the lower package consists of upper Maastrichtian to Eocene calcareous oozes and chalks. Reflectors in the upper and middle units are more chaotic than those at Site 528, indicating possible downslope transport and/or erosion. The lower package contains multiple sets of parallel reflectors that are essentially identical to Site 528 below 250 ms TWT below seafloor. The lowermost prominent reflector at 380 ms TWT below seafloor represents the K/P boundary contact at an estimated depth of ~371 mbsf (average velocity = 1.8 m/ms). Above this is a weaker reflector at 290 ms TWT below seafloor that we believe represents the P/E clay layer at an estimated depth of 276 mbsf. The reflectors above represent Eocene and Oligocene layers.
In short, coring in three holes at Site 1266 recovered a 333-m-thick section of upper Paleocene to Pleistocene calcareous-rich sediment. The advanced piston corer (APC) functioned to a depth of 250 mbsf, at which point the extended core barrel (XCB) was deployed. Significant condensed clay-rich intervals and unconformities are present in the middle and upper Eocene and the upper Miocene. Despite multiple holes, several short intervals were not recovered. Nevertheless, the P/E clay layer was recovered intact in one hole (~267 mbsf) where the XCB was used to a level just above the boundary, at which point the APC was redeployed.
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